I've heard my dad say it, my brother say it, and even my boyfriend say it. I have guy friends who say it, too. And I'm a teacher for 8th grade. The male teachers I work with aren't any different. We see when students have 'crushes' and the male teachers will comment that they know what some guys are after with the female students because they were once that age and 'know how guys think'. (It's not as creepy as it sounds... we actually have to watch student behavior to make sure no one is harassed and to know when to get parents and counselors involved. Happens a lot more often than you would think with 8th graders and sometimes really interrupts the learning process).
So... why is it okay for men to generalize men when it comes to intentions with women but it's not okay when women make the same generalization? Is it just because it's coming from a woman and not a guy?